1. Technical Field
This application relates to magnetic write heads that employ TAMR (thermally assisted magnetic recording) to enable perpendicular writing on magnetic media having high coercivity and high magnetic anisotropy. More particularly, it relates to the use of a concave leading shield configuration that enhances the strength of the magnetic write field.
2. Description
Magnetic recording at area data densities of between 1 and 10 Tera-bits per in2 involves the development of new magnetic recording media, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect. This latter effect is the thermal instability of the extremely small regions of magnetic material on which information must be recorded, in order to achieve the required data densities. A way of circumventing this thermal instability is to use magnetic recording media with high magnetic anisotropy and high coercivity that can still be written upon by the increasingly small write heads required for producing the high data density. This way of addressing the problem produces two conflicting requirements:
1. The need for a stronger writing field that is necessitated by the highly anisotropic and coercive magnetic media.
2. The need for a smaller write head of sufficient definition to produce the high areal write densities. Such a write head, disadvantageously, produces a smaller field gradient and broader field profile.
Satisfying these requirements simultaneously may be a limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that is the case, further increases in recording area density may not be achievable within those schemes. One way of addressing these conflicting requirements is by the use of assisted recording methodologies, notably thermally assisted magnetic recording, or TAMR.
Prior art forms of assisted recording methodologies being applied to the elimination of the above problem share a common feature: transferring energy into the magnetic recording system through the use of physical methods that are not directly related to the magnetic field produced by the write head. If an assisted recording scheme can produce a medium-property profile to enable low-field writing localized at the write field area, then even a weak write field can produce high data density recording because of the multiplicative effect of the spatial gradients of both the medium property profile and the write field.
The heating effect of TAMR works by raising the temperature of a small region of the magnetic medium to essentially its Curie temperature (TC), at which temperature both its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to produce within that region.
In the following, we will address a particular implementation of TAMR, namely the transfer of electromagnetic energy to a small, sub-micron sized region of a magnetic medium through interaction of the magnetic medium with the near field of a plasmon excited by an optical frequency laser. The transferred electromagnetic energy then causes the temperature of the medium to increase locally.
The plasmon is typically excited in a particularly shaped plasmon generator (PG) that is incorporated within the read/write head structure. The source of optical excitement can be a laser diode, also contained within the read/write head structure, or a laser source that is external to the read/write head structure, either of which directs its beam of optical radiation at the PG through a means of intermediate transfer such as an optical waveguide (WG). As a result of the WG, the optical mode of the incident radiation couples to a propagating edge plasmon mode in the PG, whereby the optical energy is converted into plasmon energy that travels along the PG. This plasmon energy is then focused by the PG onto the medium, at which point the heating occurs. When the heated spot on the medium is correctly aligned with the magnetic field produced by the write head pole, TAMR is achieved.
In a perpendicular magnetic recording (PMR) write head, which is now used for high density recording in magnetic media having soft magnetic underlayers (SUL), the strength of the magnetic field is already sufficient for the writing process. Therefore, in the PMR head system, it is the field gradient that must be improved. This is done by the use of shields.
In the TAMR system, however, due to defects in the media and large variations in grain sizes, a high magnetic field is desirable for good recording quality. Unfortunately, the SUL effect is much weaker due to media limitations so an alternative approach is needed to improve TAMR writability.
These issues are discussed by Hu et al. (US Publ. Pat. Appl. 2005/0083605 A1), Tanaka et al (US Publ. Pat. Appl. 2012/0084969), Takano et al. (U.S. Pat. No. 8,035,930 B2), Zhou et al. (U.S. Pat. No. 8,059,496) and Jin et al., US. Publ. Pat. Appl. 2012/0020194 (assigned to the present assignee and fully incorporated herein by reference), but an alternative approach is not provided.